It has heretofore been proposed in U.S. Pat. No. 4,740,401 to provide a cased glass stream for forming glassware having layered wall segments. Published European Applications EPO722907A2 and EPO722908A2, both assigned to the assignee hereof, disclose techniques for delivering such a cased glass stream in which core glass from a first source is delivered through a first orifice. A second orifice is vertically spaced beneath and aligned with the first orifice, and is surrounded by a chamber that communicates with the second orifice through the gap between the first and second orifices. A heated tube delivers casing glass from a second glass source to the chamber that surrounds the second orifice. Glass flows by force of gravity through the orifices from the first and second sources in such a way that a cased glass stream emerges from the second orifice. This cased glass stream may be sheared by conventional techniques to form individual cased glass gobs for delivery to conventional individual section glassware forming machines.
Although the techniques disclosed in the noted patent applications address and overcome problems theretofore extant in the art, further improvements remain desirable. For example, a problem remains concerning uniformity of distribution of casing glass thickness around the circumference of the core glass stream. The first and second glass flow orifices are provided in respective first and second orifice rings that are assembled to each other to form an orifice ring housing. The first or upper orifice ring has a peripheral flange that rests upon a ledge on the second or lower orifice ring. A pocket in the lower orifice ring cooperates with the underside of the upper orifice ring to form the metering gap between the orifices and the chamber through which casing glass flows to the metering gap. The orifice rings are preferably of high-temperature refractory composition. It has been found that the flow of glass can cause severe erosion of the upper orifice ring refractory material, as much as 0.007 inches per day. The metering gap between the orifice rings must be maintained within fairly close tolerances, on the order of about 0.10 inches, in order properly to meter and control casing glass distribution. Severe erosion of the refractory material reduces the useful life of an orifice ring housing to as little as three weeks. It has been proposed in above-noted U.S. Pat. No. 4,740,401 to provide a layer of platinum on the central flow passage, the orifice and the underside of the first or upper orifice ring to reduce or prevent erosion of the refractory material due to high temperature glass flow.
It is therefore a general object of the present invention to provide a method and apparatus for delivering a cased glass stream of the character disclosed in the above-noted applications that reduce erosion wear at the orifice ring housing, and therefore obtain an extended useful life of the orifice ring housing components. Another and more specific object of the present invention is to provide a method and apparatus for extending the useful life of the orifice ring housing components from as little as three weeks as is currently typical to on the order of six to nine months.
Apparatus in accordance with a presently preferred embodiment of the invention for forming a cased glass stream having an inner core glass surrounded by an outer casing glass includes a first orifice for receiving core glass from a first source, and a second orifice vertically spaced beneath and aligned with the first orifice. A chamber surrounds the second orifice and communicates with the second orifice through a metering gap between the first and second orifices. Casing glass is delivered from a second source to the chamber such that glass flows by gravity through the orifices from the first and second sources to form the cased glass stream. The first and second orifices are disposed in respective first and second orifice rings of refractory composition. The first orifice ring has a peripheral flange and an interior passage for glass flow from the first source to the first orifice. The second orifice ring has a peripheral ledge on which the flange rests, and a pocket for cooperating with the underside of the first orifice ring to form the chamber that surrounds the metering gap. At least the underside of the first orifice ring, and preferably the underside of the first orifice ring, the first orifice and the glass flow passage through the first orifice ring, includes a continuous layer of high-temperature erosion-resistant metallic composition such as platinum.
A method of preventing erosion of the first orifice ring in accordance with a second aspect of the present invention therefore comprises the step of lining the inner glass flow passage, the first orifice and the underside of the first orifice ring with a continuous layer of high-temperature erosion-resistant metallic composition such as platinum. The layer on the underside of the upper orifice ring preferably extends onto the peripheral flange of the upper orifice ring for disposition between the flange and its supporting ledge of the lower orifice ring to prevent glass flow erosion from eating around the edge of the layer. The platinum layer may be sprayed onto the first orifice ring, or provided as one or more separate sheets that are formed onto the orifice ring. The platinum layer preferably has a sprayed thickness in the range of about 0.005 to 0.007 inches.